I recently had a religious apologist lay the Cosmological Argument on me:
- Everything that begins to exist has a cause
- The universe began to exist
- Therefore, the universe has a cause
- And therefore, no bacon or gay sex, and women must cover their hair
The Cosmological Argument is a terrible way to try to "prove" the existence of God because every one of its premises is controversial. Precisely because of the controversial nature of its premises, it is way to start thinking about some deep questions. The Wikipedia article brings up several controversies with the argument: its circularity, its special pleading, its elevation of a posteriori scientific knowledge to a priori logical knowledge, etc. And there are even more controversies.
What, for example, does it mean to exist? Do I, Larry, the person, exist? I am, in a very deep sense, not an independent, indivisible object but rather an arrangement of atoms. All the mass that is me existed before I was born; all of it will continue to exist after I'm dead. What "exists" is just an arrangement of those atoms, and the arrangement persists even as the atoms are gradually replaced. Indeed, in a sense, all the things that we (at least those of us who are not particle physicists) talk about as "objects" are just arrangements of atoms. But "the universe" is not an arrangement of atoms. If we're using "existence" to denote particular arrangements, then the universe, which is always the universe no matter how its atoms are arranged, is not "existing" in that sense. Contrawise, if the universe exists, then we are using existence to denote something independent of arrangement, and, as far as we know, actual mass-energy does not ever "begin" to exist; all the mass-energy in the universe has always been there.
And what about abstract entities? Does the orbit of Mercury exist? Would it continue to exist if Mercury itself were to be blown apart? How about the orbit of "Vulcan," the imaginary planet exactly opposite the Sun from the Earth? Does the circle — not actual, physical things arranged in circles, but the idea of the circle — exist? How about the idea of the "gnort", a particularly interesting mathematical arrangement that human beings won't discover for another century? How about the idea of the "kerfibble", another interesting mathematical arrangement that human beings, sadly, will never discover before we and all our descendents are inevitably wiped out?
Its interesting and valuable to think about all these controversies. And that's the function of philosophy: not to discover answers but to pose interesting questions that lead us to examine our thought deeply and carefully.
One of the greatest sins of Christianity (and Islam, but curiously not really prevalent in early Judaism) is the expropriation of philosophy from the humanities to the "sciences", to use philosophy not to ask ever-deeper questions but to purport to "prove" the childish, exploitative, and fundamentally misanthropic (and especially misogynist) privilege of the Church.